Starting system for alternating current motors



Aug. 21, 1934. c. E. KILBOURNE :STARTING SYSTEM FOR ALTERNATING CURRENTMOTORS Filed Nov. 18, 1933 Fig.1.

ll'llllll 0/0 20304050 60 MQUM/W Inventor:

Charies EKHbourne b5 Attorne g.

Patented Aug. 21, 1934 STARTING SYSTEM FOR ALTERNATING CURRENT MOTORSCharles EQKilbourhe, Schenectady, N. Y., as-

signor to General Electric Company, a corporation of New YorkApplication November 18, 1933, Serial No. 698,627

7 Claims.

My invention relates-to starting systems for alternating currentmotorsand its object is to provide an improved arrangement and method forstarting polyphase motors. While my in- U vention is particularlyapplicable for starting synchronous motors, it may be used to start anyother type of polyphase machine, such as a synchronous converter, aninduction motor, etc.

One of the arrangements now in use for starting polyphasesynchronousmotors consists in first connecting a part of the armaturewinding directly to the supply circuit. .After the motor hasaccelerated, the rest of the armature winding is connected to the supplycircuit. Heretofore, there have been two generaltypes of part windingswhich have been used for these starting purposes.

One of these general types consists in providing the motor armature withtwo or more polyphase circuits with corresponding coil sides of. all ofthe circuits disposed in a predetermined manner under eachpole of themachine. One such class of windings is known as an alternate slotarrangement in which the corresponding coil sides of the two circuits ofa two-circuit winding, for example, are arranged in adjacent slots sothat when only one circuit is energized there is an energized slotfollowed by an unenerglzed slot. Such a type of winding is disclosed inChase Patent No. 1,815,832, granted July 21, 1931. Another such class ofwindings is known as an alternate phase belt arrangement inwhich in atwo-circuit arrangement, for example, a plurality of coil sides of onecircuit is arranged in a group of adjacent slotsunder each pole and acorresponding plurality of coil sides of another circuit are arranged inanother group of slots under each pole so that when only one circuitis'energized there is in each phase belt a group of energized slotsfollowed by a group of unenergized slots. Such a type of winding isdisclosed in the British Patent No. 366,184.

This general type of part winding aflects the starting characteristicsof the machine in somewhat the same manner that a reactor placed in theexternal linedoes. That is, it reduces both the starting current and thestarting torque but unfortunately the current goes down directly withthe reduction factor for the percentage of winding, used whereas thetorque goes down as the square of that factor. Therefore, this type ofwinding has the undesirable feature that the ratio between torque andcurrent, that is, the torque efliciency, is materially less when onlypart of the winding is being used than when the whole winding is beingused.

A second general type of part winding which has been used for motorstarting consists in connecting half of the poles in one circuit and Bthe other half of the poles in another circuit. In some cases alternatepoles have been connected in one circuit and the remaining poles in theother andin other cases alternate pairs of poles or alternate groups ofat least a pair6 of poles have been connected in one circuit and theremaining alternate pairs or groups of poles in the other circuit orcircuits. This second general type of part winding has the undesirablefeature that the torque curve when only one of the circuits is energizedmay have pronounced dips in it due to the presence of fields havingother than the fundamental number of poles in the magnetic structure. Ihave found that the undesirable features present in the latter of thetwo general types of part windings mentioned above can be eliminated byfirst energizing a large enough concentrated portion of the armaturewinding toeliminate or minimize these dips and then adding to thisenergized section additional adjacent sections of sufiicient size andnumber to give the desired torque and current input characteristics. Theimportant point is to increasethe amount of the total armature circuitin use by increasing the size of the energized section rather than byadding another section which is not adjacent to another energizedsection.

I find that electrically the best results would be obtained by usingthemaximum concentra- 9 tion, that is with a two-circuit 32-polemachine, for example, one circuit would energize 16adjacent poles andthe other circuit would energize the other 16 poles. This arrangement,with only one circuit energized, would produce a torque curve havingmany small dips in it but no bad ones. However, this arrangement ismechanically very bad because it concentrates all the magnetic force inone direction and may pull the shaft out of center or do otherundesirable things unless the mechanical parts are built large enough tostand the strain. Such a construction, however, results in an increasein the cost and weight of the machine. Therefore, to overcome thismechanical difliculty in cases where it is necessary to do so, Ifirst,energize diametrically opposite sections of the armature winding,each section being as large and as nearly equal to the other energizedsection as possible to give the desired starting torque and then Iincrease the 24-pole polyphase machine andsuitable switching means forstarting such a motor in accordanm with my invention and Pig. 2illustrates the current input and torque characters or a 24-polemachinestartedinaccordancewithmyinvention.

Referring to Fig. 1, I have shown an arrangement embodying my inventionior operating a 2&-

motor with one third oi the motor armature winding energised. with twothirds o! the motor armature winding energised and with all of the motorarmature winding energized. In order to simplify the disclosure, I haveshown a single slot per pole per phase arrangement. Therefore, a'l2-slot machine is shown. It will be understood, however. that myinvention is not limited to any particular integral or iractional slotper pole per phase arrangement or to any particular coil pitch.

In the particular arrangement shown, I first energize one group or iouradlacent poles and a diametrically opposite group oi (our adjacent eightpoles or one third or the total number are simultaneously energized tostart the motor. This result is obtained by closing switch 10 whichconnects the polyphase coil gro pin s l2, 13, 14 and 15 to the polyphasesupply circuit 10. The coil groupings 12-15 inclusive are respectivelydisposed on the magnetic structure oi the machine in any suitable mannerwell known intheartscastoproducethetwoadlacent poles P-1 and P-2. thepoles P-3 and P-4 and the diametrically opposite poles P-l3 and P-lt andpoles P-iii and 3-16.

Incrdertoenergisetwothirdsotthearmature winding, 1 increase eachenergized section so that it includes eight poles. This may be done in anumber of ways. For example, the adiacent group of poles 2-5 to P-8inclusive and the diametrically opposite group oi poles P-l'l to P-inclusive may be added respectively to group P-l to P-4 inclusive andP-l3 to P-ld inclusive or the adjacent group oi poles P-ill m P-24 andthe diametrically opposite group of poles P-D tor-12 inclusive may beadded respectively to the group of poles P-l to P-4 inclusive and 9-18to P-ls inclusive. Such a grouping of poles, however, shifts themagnetic center 0! each energised group,which in some cases may beobjectionable; Therefore in order to avoid any such objection, I haveshown an arrangement whereby the closing 0! a switch 20 connects to thesupply circuit 16 the polyphase coil groupings 21, 2'), 28 and 24 whichare arranged on the magnetic structure of the motor in any suitablewell-known manner so that they respectively iorrnthe poles P-5 and P-B,the poles 2-11 and P 12, the poles P-17 and P-ls and the poles P-23 andP-24. Therefore, it will be seen that each energised sectionor i'ourpoleshas increased in sine to an energized section-oi eight poles byenergizing the adjacent pairofpoles ateachendthereoi. Inthis manner themagnetic'center line has not been shifted.

The remaining poles of the machine may be energized by closing a switchwhich connects the remaining coil groupings 31, 82, 33 and 34 to thesupply czrcuit 10. These coil groupings 31-34 inclusive may be arrangedin any suitable mannersothatwhentheyareenergiaedthey form the poles 8-!to P-lO inclusive and the poles P-19 to P-22 inclusive.

while I have shown manually controlled switches 10, 20 and 30 forconnecting the various polyphase coil groupings of the machine to thepolyphase supply circuit 16, it will be evident to those skilled in theart that any suitable automatic means may be employed for eiiecting theoperation 0! these switches in the proper sequence and at the propertime. For example, any suit!- able speed control or time control means.examplesoiwhichareweilknowninthearhmaybe employed for eiiecting theclosing of the switches 20and3o inresponsetopredeterminedspeedsol themachine or after a predetermined time lapse.Alsoitwillbeevidenttothoseskilledinthearttbatiithemachinebeingstartedisasynchronous motor, any suitable means maybe provided for connectingtheiieldwinding thereoitoasuit- 1U able sourceoi direct current in order to pull the motor into syncbronism at theproper time during the starting operation.

Fig. 2 shows the actual torque and line current characteristics of azi-pole machine obtained 10 by energizing the various poles thereof inthe manner outlined above. It will be noted that the ratio of current totorque at any given speed is substantially the same in each case andthat there are no bad dips in the torque curves when only lid part ofthe winding is being used. Thereiore, there is no danger of the motorstalling during the starting operation.

My investigations show that the windings iormingsnenergisedsectionshouldatailtimesbelll concentrated as much as possible in order to eliminatethe elect/of harmonic fields on the torquecurveandatthesametimetheenergisedwindings should be so placed that themagnetic unbalshoe is as small as possible. Consequently, 1 10 find thatthe best practical arrangement is tostartthemachinebyenergimngtwodiametrical- 1y opposite substantiallyequal sections oi the armature winding and then increasing the aims ofthese two sections in a predetermined order in I order to obtain thedesired increases in torque as the motor accelerates. It will beobserved. however, that in some cases it is impossible to have exactlythe same number of poles in both of the emrgized sections. l'or example,in order no to start a iii-pole machine with half of the windingenergized. it is necessary to start with 1'7 poles energised. This maybe done by energizing e poles in one of the two diametrically oppodtesections and 9 poles in the other.

My investigations further show that when machines having 8 poles or 1cmare started in accordanoe with my invention the two diametricallyopposite groups or poles constitute so few poles that the harmonics inthe magnetic field reach such a substantial else as to produce ratherbad dips in the torque curve. Therefore, my invention isoi particularutility in connection with machines having ten or more poles and isespechlly adapted tor use in machines having a large num- 1 her dipoles.such assixteen or more poles, as it provides an arrangement forincreasing the two diametrically opposite groups in a largenumberorstepsthusensblingamotortobestartedwim thecurrentinputaintsinedatsutimssdm-iagtlc the starting operation within predeterminednarrow limits. For example, a forty-eight pole machine may be started insix equal steps by first energizing two diametrically opposite groups oftour adjacent poles, then successively increasing the number of poles ineach group to eight, twelve, sixteen, twenty and twenty-four.

While I have, in accordance with the patent statutes, shown anddescribed my invention as applied to a particular system and asembodying various devices diagrammatically indicated, changes andmodifications will be obvious to those skilled in the art and I,therefore, aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope oi my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. The method of starting a polyphase motor comprising a plurality oipolyphase primary coil groupings distributed on the magnetic structureof the motor so that each primary grouping forms at least one magneticpole, which consists in energizing the groupings forming twodiametrically opposite substantially equal groups of adjacent poles, thenumber of poles in each such group being less than hall the total numberof poles, and then increasing the sizes of said groups a plurality oftimes by energizing the remaining windings in a predetermined order.

2. The method of starting a polyphase motor having more than eight polesand comprising a plurality of polyphase primary coil groupingsdistributed on the magnetic structure 01 the motor so that each primarygrouping forms at least one magnetic pole, which consists in energizingthe groupings forming only two diametrically opposite substantiallyequal groups of adjacent poles, the number oi poles in each such groupbeing less than half the total number of poles, and then simultaneouslyincreasing a plurality of times the number of poles in each group byenergizing certain oi the remaining groupings.

3. The method of starting a polyphase motor having more than eight polesand comprising a plurality of polyphase primary coil groupingsdistributed on the magnetic structure oi the motor so that each primarygrouping forms at least one magnetic pole, which consists in energizingthe 1 grouping forming only two diametrically oppolite substantiallyequal groups of adjacent poles,

the number of poles in each such group being less than half the totalnumber of poles, and then simultaneously energizing a portion of theremaining groupings so as to form diametrically opposite groups of polesadjacent to each group of said first mentioned diametrically oppositegroups so as to increase the sizes thereof in substantially equalamounts.

4. The method or starting a polyphase motor having more than eight polesand comprising a p 3 plurality oi polyphase primary coil groupingsdistributed on the magnetic structure of the motor so that each primarygrouping forms at least one magnetic pole, which consists in energizingthe groupings forming only two diametrically opposite substantiallyequal groups of adjacent poles, the number of poles in each such groupbeing less than half the total number of poles, and then increasing thenumber of poles in each group in a plurality of steps by energizing thegroupings forming said additional poles in a predetermined order untileach group comprises substantially half the total number of poles.

5. In combination, a polyphase motor of more than eight poles andcomprising a plurality of polyphase coil groups distributed on itsmagnetic structure so that each grouping forms at least one magneticpole, a polyphase supply circuit, and means for starting said motorincluding means for connecting only the groupings forming twodiametrically opposite substantially equal groups of poles containingless than half the total number of poles to said supply circuit, andmeans for energizing in a plurality 01' steps the group ings forming thepoles adjacent to each of said groups of poles in order to increase thenumber of poles therein in a predetermined order.

6. In combination, a polyphase motor of more than eight poles andcomprising a plurality of polyphase coil groupings distributed on itsmagnetic structure so that each grouping forms at least one magneticpole, a polyphase supply circuit, and means for starting said motorincluding means for connecting only the groupings forming twodiametrically opposite substantially equal groups 01 poles containingless than half the total number of poles to said supply circuit, andmeans for simultaneously energizing the groupings forming adiametrically opposite group 01' poles adjacent to said first mentionedgroups and containing less than the total number of remaining poles inorder to increase the sizes of said first mentioned group insubstantially equal amounts.

7. In combination, a polyphase motor of more than eight poles andcomprising a plurality of polyphase coil groupings distributed on itsmagnetic structure so that each grouping forms a magnetic pole, apolyphase supply circuit, and means for starting said motor includingmeans for connecting only the groupings forming two diametricallyopposite substantially equal groups 01' poles containing less than halfthe total num ber 01' poles to said supply circiiit, and means forsuccessively energizing in a predetermined order 3 the groupings formingpoles adjacent to each of said first mentioned groups until each of saidgroups comprises substantially half the total number of poles.

CHARLES E. KILBOURNE.

